Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

Evaporator tubes

2. In a lithium bromide absorption refrigeration system

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

3. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

4. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Detect liquid in vapour

5. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

6. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

3.33

4.33

2.33

7. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Water coolers

All of these

Room air conditioners

8. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

9. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

10. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Carnot

Rankine

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11. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Brine

Freon

12. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

Compressor and condenser

13. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.4

0.6

0.67

14. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

15. A bootstrap air cooling system has

Four heat exchangers

Two heat exchangers

One heat exchanger

Three heat exchangers

16. For obtaining high COP, the pressure range of compressor should be

Any value

Low

High

Optimum

17. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

18. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Sub-cooling or under-cooling

Super-cooling

None of these

19. Which of the following cycles uses air as the refrigerant?

Stirling

Ericson

Bell Coleman

Carnot

20. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 1

1: 3

9: 1

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21. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Axial

Piston type reciprocating

22. Most thermostatic expansion valves are set for a superheat of

5°C

15°C

10°C

20°C

23. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

24. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

Low boiling point

High risibility with oil

25. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

26. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

27. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

28. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Involves no change in volume

Takes place at constant temperature

Takes place at constant entropy

29. Rating of a domestic refrigerator is of the order of

40 tons

5 tons

0.1 ton

10 tons

30. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always less than unity

Always more than unity

Page 4 of 4

31. The boiling point of ammonia is

-33.3°C

-30°C

-77.7°C

-10.5°C

32. Freon group of refrigerants are

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

Toxic

33. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

34. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

35. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

30 bar

15 bar

8 bar

36. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

37. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

38. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

39. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Positive

None of these

Zero

40. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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